1. Field of the Invention
The present invention relates to a method of manufacturing an opto-electronic module of the receptacled type often used in optical transmission systems. More specifically, the invention relates to the receptacle structure of the module, and to a fixture for immobilizing the receptacle during the assembly process.
2. Description of the Related Art
One common type of receptacled opto-electronic module is a coaxial laser diode module including a laser diode unit, a receptacle, and a sleeve. In the assembly process, the receptacle and the laser diode unit are held in respective fixtures, the sleeve is mounted on the receptacle, and the laser diode unit is optically aligned with the receptacle and sleeve. The alignment is performed by supplying power to the laser diode unit and measuring the optical output obtained through an optical fiber coupled to the receptacle. When satisfactory optical output is obtained, the sleeve is spot-welded to the receptacle and laser diode unit, securing these three parts in the correctly aligned positions.
A problem is that the welding process can disturb the optical alignment. In the inventor""s experience, in about twenty to thirty percent of the coaxial laser diode modules assembled in the above way, the optical output obtained after the welding step is at least two decibels (2 dB) less than the optical output obtained in the alignment step. In extreme cases, the optical output falls below the specification value, causing the module to be rejected. Even in less extreme cases, the output characteristics may be degraded to the point that the module fails a reliability test and is rejected for that reason. As a result, the yield of the manufacturing process is lowered, and the manufacturing cost per module is increased.
An object of the present invention is to prevent the welding step in the assembly of a receptacled opto-electronic module from disturbing the optical alignment of the receptacle and the opto-electronic unit.
The invention provides a method of manufacturing an opto-electronic module having an opto-electronic unit for generating a light beam and a receptacle for attachment of a cable into which the light beam is optically coupled. In the invented method, an indentation is formed in the receptacle, and the receptacle is held in a first fixture having a projecting lip that fits into the indentation. The opto-electronic unit is held in a second fixture and is optically aligned with the receptacle. The receptacle and opto-electronic unit are then fastened together by welding.
During the welding process, the projecting lip of the first fixture keeps the receptacle from moving toward the opto-electronic unit, so that the receptacle is held immobilized and the optical alignment is preserved.
The opto-electronic module manufactured by the method of the invention includes an opto-electronic unit for generating a light beam and a receptacle for attachment of an optical fiber cable into which the light beam is optically coupled. The receptacle is secured to the opto-electronic unit by welding, and has an indentation enabling the receptacle to be held in the first fixture to immobilize the receptacle during the welding process.
The receptacle may have a generally cylindrical shape with a first end and a second end, the first end being attached to the opto-electronic unit. The indentation may be formed by a reverse taper of the second end, or by a rectangular groove running around the second end. The opto-electronic module may also include a sleeve, the receptacle being welded to the sleeve and the sleeve being welded to the opto-electronic unit.
The opto-electronic module may be a coaxial laser diode module.
The first fixture used in the manufacturing method of the invention holds the receptacle of the opto-electronic module, first while the receptacle is being optically aligned with an opto-electronic unit of the opto-electronic module, then while the receptacle is being fastened to the opto-electronic unit by welding. The first fixture has a projecting lip fitting into an indentation in the receptacle to immobilize the receptacle during said welding.
The first fixture may include a flat part and a V-shaped part, the receptacle being held between the flat part and the V-shaped part. The projecting lip may be present in both the flat part and the V-shaped part, and may have a trapezoidal or a rectangular sectional shape.